This invention relates to a process for separating olefins from saturated hydrocarbons followed by separating linear alpha olefins and internal olefins from a saturated hydrocarbon stream.
Many industrial processes produce olefin/saturated hydrocarbon streams that are mixtures of olefins, saturated hydrocarbons, and oxygenates. Olefins are frequently used in the manufacture of polymers such as polyethylene, as drilling mud additives, or as intermediates for the production of oil additives and detergents. Some industrial processes manufacture olefin streams by oligomerizing ethylene over an alpha olefin catalyst to produce mixtures of alpha and internal olefins having a broad range of carbon numbers. However, these streams rely on the use of ethylene as a feedstock material, which add a significant cost to the manufacture of the olefin. On the other hand, the FT process starts with an inexpensive feedstock, syngas, generally derived from natural gas, coal, coke, and other carbonaceous compounds to make oligomers comprised of olefins, aromatics, saturates, and oxygenates.
The FT process, however, is not very selective to the production of olefins. While reaction conditions and catalysts can be tuned to manufacture a stream rich in the desired species within the FT product stream, a large percentage of the FT stream contains other types of compounds which must be separated from the olefins, which olefins are purified, and then sold into different markets. For example, a typical commercial FT stream will contain a mixture of saturated hydrocarbons, olefins, aromatics, and oxygenates such as organic carboxylic acids, alcohols, ethers, esters, ketones, and aldehydes. All these compounds must be separated from the crude FT stream before a particular composition may be offered commercially. To further complicate the separation operation, the FT stream contains compounds having a wide spectrum of carbon numbers, as well as a wide variety of olefins, ranging from C2-C200 species, internal linear olefins, alpha linear olefins, internal branched olefins, alpha branched olefins, and cyclic olefins, many of which have similar molecular weights. Separating and isolating these species is no easy task. Conventional distillation methods are frequently inadequate to separate species having closely related boiling points.
Various processes have been proposed to efficiently separate the different species in an FT stream with sufficient purity that a particular composition is acceptable in the intended application. These processes for separating out different species in an FT stream include the use of molecular sieves, which are restricted to a feed have an average carbon number range which is more limited than a composition containing a broad spectrum of average carbon numbers ranging from C5-C20, to the use of exchange resins, to the use of super-fractionators often operated at high pressure, and the use of oligomerization catalysts or etherification techniques to alter the boiling points of the species in the FT stream. Many reactive methods for separating species in an FT stream do not, however, selectively react with olefins while simultaneously reject paraffins.
U.S. Pat. No. 4,946,560 described a process for the separation of internal olefins from alpha olefins by contacting a feedstock with an adducting compound such as anthracene to form an olefin adduct, separating the adduct from the feedstock, dissociating the olefin adduct through heat to produce anthracene and an olefin composition enriched in alpha olefin, and separating out the anthracene from the alpha olefin. This reference does not suggest the desirability or the capability of anthracene to separate olefins from saturated hydrocarbons or linear alpha olefins from saturated hydrocarbons.
Once olefins are separated from saturated hydrocarbons, it would also be desirable to purify the removed saturated hydrocarbons and extract as much remaining olefin from the removed saturated hydrocarbon as possible.
This invention relates to a process for separating olefins from saturated hydrocarbons, and thereafter further treating the olefins to separate olefins from a stream of saturated hydrocarbons. The process of the invention is well suited to treating a FT stream.
In particular, there is provided a process for treating a feedstock composition comprising linear alpha olefins, internal olefins, and saturated hydrocarbons, comprising:
a) contacting the feedstock composition with a linear polyaromatic compound in a first reaction zone under conditions effective to form a reaction mixture comprising linear polyaromatic compound-olefin adducts and saturated hydrocarbons;
b) separating the first linear polyaromatic compound-olefin adducts from the saturated hydrocarbons in the reaction mixture to form an adducted olefin stream and a first saturated hydrocarbon stream enriched in the concentration of saturated hydrocarbons over the concentration of saturated hydrocarbons in the feedstock composition;
si) contacting the saturated hydrocarbon stream with a linear polyaromatic compound in a second reaction zone under conditions effective to form a reaction mixture comprising second linear polyaromatic compound-olefin adducts and saturated hydrocarbons;
sii) separating the second linear polyaromatic compound-olefin adducts from the saturated hydrocarbons in the reaction mixture to form a second adducted olefin stream comprising the second linear polyaromatic compound-olefin adducts, and a second saturated hydrocarbon stream enriched in the concentration of saturated hydrocarbons over the concentration of saturated hydrocarbons in the first saturated hydrocarbon stream;
siii) dissociating the second linear polyaromatic compound-olefin adducts to form linear polyaromatic compounds and a second olefin composition comprising alpha olefins and internal olefins enriched in the concentration of alpha olefins and internal olefins over each of their concentrations in the first saturated hydrocarbon stream.